(i) Field of the Invention
The present invention relates to a hydrogen preparing apparatus in which a hydrogen-containing gas can be produced by reforming a hydrocarbon and/or a hydrocarbon containing an oxygen atom such as methane, propane, methanol, ethanol or petroleum with steam or the like, and hydrogen alone can be selectively and efficiently separated from the produced hydrogen-containing gas.
(ii) Description of the Related Art
In a hydrogen preparing apparatus utilizing a steam reforming reaction, hydrogen, carbon monoxide and carbon dioxide are produced from a material gas comprising a hydrocarbon such as methane or methanol by the use of a reforming catalyst:
(In the case of methanol) EQU CH.sub.3 OH+H.sub.2 O.fwdarw.CO.sub.2 +3H.sub.2 ( 1) EQU CH.sub.3 OH.fwdarw.CO+2H.sub.2 ( 2)
Furthermore, if necessary, hydrogen is separated from this produced gas.
The above-mentioned reforming reaction is an endothermic reaction, and so the higher reaction temperature is, the more smoothly the reaction proceeds. However, under the high temperature conditions, a hydrocarbon such as methane, methanol, or carbon monoxide cracks to deposit carbon, so that the catalytic activity of the reforming catalyst deteriorates inconveniently. As a technique for preventing this carbon deposition, there has been used a method in which the reaction is carried out by feeding a large amount of steam, but in this case, additional heat is uneconomically required to generate the steam.
Heretofore, in order to solve these problems, a hydrogen separating type steam reforming reactor, in which the hydrogen separation and the reforming reaction are combined, has been suggested for the purposes of lowering the reaction temperature and advancing the reaction (e.g., Japanese Patent Application Laid-Open No. 40701/1994).
This reactor contains hydrogen separating films for selectively separating hydrogen in a steam reforming reaction catalyst layer, and in the reaction, hydrogen generated by the reforming reaction is successively separated from the reaction system by the hydrogen separating films, whereby the reaction can proceed even at a low temperature.
Such a hydrogen separating type reforming reactor can produce high-purity hydrogen, and so it is considered that this type of reactor is applied to a fuel battery. Particularly in a phosphate type or a solid polymeric type fuel battery, Pt which is an electrode catalyst is poisoned with a trace amount of CO, and in the solid polymeric type fuel battery, Pt is poisoned, even if the concentration of CO is as low as 10 .mu.m. Therefore, it is necessary to remove CO from the reformed gas. Hence, the application of the above-mentioned reactor capable of producing high-purity hydrogen is preferable.
However, the reforming catalyst which can be used in the above-mentioned hydrogen separating type reforming reactor is usually in the state of spherical or pelletlike grains, and therefore in order to obtain the surface area of the catalyst necessary for the reforming, a large amount of the catalyst is required to be filled, which leads to the enlargement of the apparatus. Since the large amount of the catalyst is filled, a distance between a catalyst layer and the hydrogen separating film is prolonged, so that it is difficult to separate hydrogen which is present apart from the hydrogen separating film and the very long reactor is required (Japanese Patent Application Laid-Open No. 295402/1988). If the spherical or pelletlike catalyst is ground and filled, the structure of the catalyst becomes irregular, so that the filling density becomes nonuniform, with the result that sufficient catalytic characteristics cannot be obtained (Japanese Patent Application Laid-Open No. 105901/1987).
Furthermore, when such a hydrogen separating type reforming reactor is exposed to such conditions as to suffer vibration, for example, when the reactor is mounted on an electromobile as a hydrogen fuel preparing apparatus for the electromobile having a fuel battery system, the catalyst breaks and the filling state of the catalyst changes sometimes by the vibration, so that the efficiency of the catalyst deteriorates inconveniently.